Light-sensitive resist which can be developed in an aqueous-alkali manner and operates negatively

ABSTRACT

The invention relates top a light sensitive, aqueous alkali developing, negatively acting resist, comprising a phenolic resin as a binder, and a diazostilbene disulfonic acid ester light sensitive component, a solvent or mixture of solvents, and film forming and/or film stabilizing additives, and to a process for preparing the light sensitive component.

FIELD OF THE INVENTION

The invention relates to a light sensitive, aqueous-alkali developing,negatively functioning resist.

BACKGROUND

The greatest part of commercially available negatively functioningphotoresists are in a nonaqueous form. Since in the case of theseresists also in the case of resist processing, especially in thedevelopment of the illuminated resist areas, special organic solventshave to be used, the interest in their use is constantly reduced due totheir increased environmental damage, and their limited performanceparameter caused by the swelling of the resist during development (lackof dimensional stability in the transfer of the structural mask in theresist) [H. Böttcher; J. Bendig; M.-A. Fox; G. Hopf; H.-J. Timpe:Technical Applications of Photochemistry, Publ. Verlag fürGrundstoffindustrie, Leipzig 1991, p. 178ff].

The Raycast-Series are used as aqueous alkali developing, nonswelling,negatively functioning photoresists [S. Nonogaki: Polym. J. 19 (1987),p. 99], and the Waycoat Resists [M. A. Toukhy; S. F. Mariotte: SPIEAdvances in Resist Technology and Processing (1984), p. 86].

The main components of the Raycast-Series (with the resists RD 2000N,1000N, and RG 3000N) polyvinylphenol (PVPh) is the polymeric binder, aresist-specific azide or bisazide as light sensitive components, and2-methoxyacetate as solvent. The resist RD 2000N is used in the deepUV-range (DUV). The resists RU 1000N and RG 3000N are most sensitive inthe UV range (308 nm, 313/320 nm, 365 nm) respectively in the UV/Visrange (365 nm, 406 nm, 436 nm). The light sensitive components in theresists RU 1000N and RG 3000N have only a limited solubility in thepolymer solution, therefore the resists have a low solids content,suitably from 5% to 50% wt., most suitably from 5% to 35% wt. Themaximum achievable film thicknesses of the resist applied to a substrateis 2 μm.

PVPh has an excellent solubility, especially in the customary resistsolvents but the high production costs represent a great drawback.

The Waycoat-resists are comprised of a novolac base as the polymericbinder. The employed novolac has only a small etching stability comparedto basic solutions. The solvent is very toxic. The resist is sensitivein the DUV range.

DESCRIPTION OF THE INVENTION

The object of the invention includes the preparation of a lightsensitive, aqueous alkali developing, negatively functioning resistcomprised of a polymeric binder having good solubility properties, and ahigh etching stability, and a light sensitive component, which has ahigh sensitivity and high photoreactivity over a wide spectral range,and has good solubility characteristics in the polymeric solution, andits light sensitive components can be prepared by an economical process.

The present invention is a light sensitive, acqueous alkali developing,negatively acting resist, comprising a phenolic resin as binder, a lightsensitive component of a diazostilbene-disulfonic acid ester of Formula(I)

wherein R¹ is a residue of Formula (II)

wherein R² and X are independently of each other hydrogen, or a branchedor straight chain alkyl residue, and n is a cardinal number from 1 to10, a solvent or mixture of solvents, and film forminmg and/or a filmstabilizing additive.

The invention also relates to a process for producing thediazostilbene-disulfonic acid ester light sensitive component, whichcomprises sulfochlorinating a diazostilbene disulfonic acid disodiumsalt with thionyl chloride, suitably an excess of thionyl chloride, sothat a stoichiometric amount of the dimethylformamide based on theamount of the disodium salt is employed, and reacting in the presence ofacid binding additives the resulting diazostilbene disulfochloride withan alcohol of Formula III

wherein R² is hydrogen, a branched and unbranched alkyl residue, X ishydrogen, a branched or unbranched alkyl residue, and n is a cardinalnumber from 1 to 10.

The invention also relates to a process for the lithographic productionof negative structures for the μm -and -nm range, characterized in thata photoresist is employed, which comprises a phenolic resin, alight-sensitive component of Formula (I), a solvent or solvent mixture,and film forming or film stabilizing additives, applying the resist as afilm to the substrate, the film being suitably formed on the substrateby spincoating, roller coating, moistening coating, spray coating, ordip coating to form a resist film suitably of from 0.3 μm to 10 μmthickness, drying the resist film suitably from 1 minute to 60 minutesay from 60° C. to 120° C., exposing the resist film to an image in thewavelength range of 200 nm to 400 nm suitably with a high pressure lampor a laser, developing the film with an aqueous alkaline developer,suitably an alkali metal ion-containing developer at a concentration offrom 0.2% wt. to 1.5% wt., or in a metal ion-free developer of aconcentration of from 1% wt. to 5% wt. suitably for a period of from 10to 15 minutes, and drying the resulting structure.

As the polymeric binder, a novolac(phenol-formaldehyde/cresol-formaldehyde condensate) can be employed asan alternative to the PVPh. This novolac is substantially less costly touse; it is soluble in acetone and in aqueous alkaline solutions.

Nontoxic solvents are advantageously used in the resist, suitably in theform of esters, ketones, alcohols or mixtures thereof.

In producing the light sensitive component, suitably p[yridine, NaOH, ora caustic alkali is added to the reaction mixture.

The diazidostilbene-disulfonic acid ester light sensitive component hasexcellent solubility in the aforementioned solvents and in the polymersolution, which enables a high solids content in the resist. Due to thehigh photoreactivity and the broad spectral sensitivity of thesecompounds in the range of 200 to 400 nm (DUV -and UV range) theillumination of the resist layers is possible by using the currentlyused quartz optics and with the customary glass optics.

The solids content of the resist and thus the content of light sensitivecomponents in the solids is variable within wide ranges so that asdesired film thicknesses can be obtained from 0.3μm to 10 μm.

The resist can suitably further contain surfactants, smoothers, oradhesives as filmforming and/or film stabilizing additives.

The cost advantageous synthesis of a diazostilbene-disulfonic acid esterlight sensitive component can be carried out in a simple two-stepprocess, with high yield.

The use of environmentally friendly and nontoxic, aqueous developers isof particular advantage.

The resist of the invention is suitable for use in standard(AZ-compatible) lithographic processes, to create microstructures to aresolution of <0.5 μm, which have a high dimensional stability (1:1transfer of the structure of the mask in the resist), high edgesharpness, and very good etching stability.

The invention is disclosed in more detail by way of the followingexamples.

EXAMPLE 1

42 g novolac (m-cresol/p-cresol/formaldehyde resin) is stirred at roomtemperature into the reaction product of 144 g ethyllactate and 0.028 gpolyether modified polymethylsiloxane, until the polymer is dissolvedand a clear solution is obtained. 14 g4-4′-diazidostilbene-2,2′-di(sulfonic acid butoxyethylester) is stirredinto the solution, until a reddish, clear solution is obtained. 200 gresist is obtained with a solids content of 28% wt.

EXAMPLE 2

84 g novolac (o-cresol/p-cresol/formaldehyde resin) is stirred at roomtemperature into the reaction product of 145 g ethyllactate and 0.052 gpolyether modified polymethyldisiloxane, until the polymer is dissolvedand a clear solution is obtained. Then 21 g4,4′-diazidostilbene-2,2′-di(sulfonic acid butoxyethylester) is stirredinto the solution until a clear solution results. 250 g resist isobtained with a solids content of 42% wt.

EXAMPLE 3

124 g poly(p-hydroxystyrene) is dissolved at room temperature withstirring, in the reaction product of 345 g ethylglycolacetate and 0.078g polyether modified polymethyldisiloxane. Then 31 g4,4′-diazidostilbene-2,2′-di(sulfonic acid butoxy-ethylester) is stirredin until a clear solution is obtained. 500 g resist is obtained with asolids content of 31% wt.

EXAMPLE 4

82 g novolac is stirred into 409 g ethyllactate modified with 0.044 gpolyether modified polydimethylsiloxane until a complete dissolution ofthe resin, and a clear solution is obtained. Then 7 g4,4′-diazostilbene-2,2′-di(sulfonic acid ethoxy-ethylester) is stirredin until a clear solution is obtained. 100 g resist is obtained with asolids content of 28% wt.

EXAMPLE 5 Synthesis of the 4,4′-Diazostilbene-2,2′-di(Sulfonic AcidButoxyethylester)

20 g (0.037 mol) 4,4′-diazostilbene-2,2′-disulfonic acid sodium salttetrahydrate is reacted in 100 ml (1.39 mol) thionyl chloride in a 250ml round flask with reflux cooler and gas relief pipe, in approx. 0.2 MNaOH solution) while stirring at room temperature, with 12 ml (0.155mol) dimethylformamide (DMF). After the reaction is concluded (approx. 2hours), the thionyl chloride excess is carefully centrifuged off(vacuum, 50° C.), and the yellow mass is poured onto ice water(exhaust!), sucked off, and washed several times with water.

Yield: 17.5 g 4,4′-diazostilbene-2-2′-disulfochloride.

M.P. 195 . . . 197° C., yellow crystals.

Elemental analysis: C₁₄H₈N₆O₄S₂Cl₂ (458.9); calc. C 36.6; H 1.74; N18.4; S 13.9; Cl 15.44; found C 35.5; H 1.89; N 17.8; S 13.9; Cl 14.8.

2.3 g (5×10⁻³ mol) 4,4′-diazostilbene-2,2′-disulfochloride is suspendedin 9.4 g (8×10⁻² mol) butoxyhexanol. During the proportional addition of1.5 g freshly made, fine, powdered KOH the temperature should not exceed4-5° C. After a 2-3 hour stirring the precipitate is sucked off, washedwith water, and recrystallized in ethanol.

Yield: 2.2 g 4,4′-diazostilbene-2,2′-disulfonic acid butoxyethylester).

Elemental analysis C₂₆H₃₄N₆S₂O₈ (622.72) calc. C 50.1; H 5.45; N 13.5; S10.27; found C 49.9; H 5.40; n 13.6; S 10.53.

EXAMPLE 6 Synthesis of the 4,4′Diazostilbene-2,2′-di(Sulfonic AcidEthoxyethylester)

2.3 g (5×10⁻³ mol) 4,4′-diazostilbene-2,2′-disulfochloride of Example 5,is suspended in 5.9 g (8×10⁻³ mol) ethoxyethanol. During theproportional adding of 1.5 g freshly prepared, fine, powdered KOH thetemperature should not exceed 4-5° C. After about 2-3 hours of steadystirring the precipitate is sucked off, washed in water, andrecrystallized from ethanol.

Yield 2 g 4,4′-diazostilbene-2,2′-di(sulfonic acid ethoxyethylether).

Yellowish-white crystals.

Elemental analysis C₃₃H₂₆N₆S₃O₈(566) Calc. C 46.6; H 4.59; N 14.8; S11.3; Found C 46.9; H 4.39; N 14.6; S 11.63.

EXAMPLE 7

2″-Si wafer is spincoated with a layer thickness of 1.5 μm for 30seconds at 3000 min⁻¹ with the resist of Example 1. The layers obtainedare dried at 80° C. for 2 minutes on a hotplate, and then exposed to animage with a high pressure mercury vapor lamp (=365 nm) for 60 secondswith a performance density of P=10.8. mW cm⁻².

The exposed layers are developed in 50 seconds with 0.8% wt NaOH, anddried for 15 seconds with nitrogen.

EXAMPLE 8

Resist layers prepared according to Example 7 are exposed to an imagefor 40 seconds with a high pressure mercury vapor lamp (=365 nm) with aperformance density of P=10.8 mW cm⁻² and exposed to an image. Theexposed layers are developed for 70 seconds with a 2.5% wt.tetramethylammonium hydroxide solution, and dried under a nitrogencurrent for 15 seconds.

EXAMPLE 9

Resist layers prepared and exposed according to Example 8 are developedfor 35 seconds in a 3,3% wt. tetramethylammonium hydroxide solution, anddries for 15 seconds in a nitrogen current.

EXAMPLE 10

4″-Si wafers are spincoated in 30 seconds at 3,000 min⁻¹ with a resistaccording to Example 2 (layer thickness 4.7 μm). The resulting layersare dried for 30 minutes at 95° C. in an oven. Then the layers areexposed for 60 seconds with an image by a high pressure mercury vaporlamp (=365 μm) having a performance density of 9.5 mW cm⁻².

The exposed layers are developed for 3 minutes with 0.8% wt. NaOH, anddried for 25 seconds in a nitrogen current.

EXAMPLE 11

4″-Si wafers are coated and exposed as in Example 10, and are developedfor 4 minutes and 45 seconds with a 2.5% wt. tetramethylammoniumhydroxide solution, and dried in a nitrogen current for 25 seconds.

EXAMPLE 12

4″-Si wafers are coated and exposed as in example 10, and then aredeveloped in 3 minutes in a 3.3% wt. tetramethylammonium hydroxidesolution, and dried in a nitrogen current for 25 seconds.

What is claimed is:
 1. A light sensitive, aqueous alkali developing,negatively acting resist, characterized in that the resist contains aphenolic resin as a binder, a diazostilbene disulfonic acid ester lightsensitive component of Formula (I),

wherein R¹ is a residue of Formula (II)

wherein R² and X are independently of each other hydrogen or a branchedor straight chain alkyl residue, and n is a cardinal number from 1 to10, a solvent or mixture of solvents, and film forming and/or filmstabilizing additives.
 2. A light sensitive, aqueous alkali developing,negatively acting resist according to claim 1, characterized in that theresist contains a phenol-formaldehyde- or cresol-formaldehyde condensateor a substituted or unsubstituted polyvinylphenol, or mixtures thereofas a polymeric binder.
 3. A light sensitive, aqueous alkali developing,negatively acting resist according to claim 1, characterized in that theresist has a solids content of from 5% to 50% wt.
 4. A light sensitive,aqueous alkali developing, negatively acting resist according to claims1 and 3, characterized in that the resist contains in the lightsensitive component a solids content of from 5% wt. to 35% wt.
 5. Alight sensitive, aqueous alkali developing, negatively acting resistaccording to claim 1, characterized in that the resist contains esters,ketones, alcohols, aromatics, ethers or mixtures thereof as a solvent.6. A light sensitive, aqueous alkali developing, negatively actingresist according to claim 1, characterized in that the resist containssurfactants, smoothers, or adhesives, as film forming and/or filmstabilizing additives.
 7. A process for producing a light sensitivecomponent of Formula (I) of claim 1, for a light sensitive, alkalideveloping, negatively acting resist, which comprises sulfochlorinatinga diazostilbene disulfonic acid disodium salt with thionyl chloride sothat a stoichiometric amount of the dimethylformamide based on theamount of the disodium salt is employed, and reacting in the presence ofacid binding additives the resulting diazostilbene disulfochloride withan alcohol of formula (III),

wherein R² is hydrogen, a branched and unbranched alkyl, X is hydrogen,branched or unbranched alkyl, and n is from 1 to
 10. 8. A process forproducing the light sensitive component of claim 7, which comprisesemploying an excess of thionyl chloride.
 9. A process for producing alight sensitive component of claim 7, which comprises adding pyridine,NaOH, or a caustic alkali to the reaction.
 10. A process for thelithographic production of negative structures for the μm -and -nmrange, characterized in that a photoresist is employed, which comprisesa phenolic resin, a light-sensitive component of the general formula Iwith the values mentioned above for R¹, R², X, and n, a solvent orsolvent mixture, and film forming or film stabilizing additives,applying the resist as a film to the substrate, drying the resist film,exposing the resist film to an image in the wavelength range of 200 nmto 400 nm, developing the film with an aqueous alkaline developer, anddrying the resulting structure.
 11. A process for the lithographicproduction of negative structures for the μm -and nm range according toclaim 10, characterized in that a film is formed on the substrate byspincoating, roller coating, moistening coating, spray coating, or dipcoating.
 12. A process for lithographic production of negativestructures, for the μm -and -nm range according to claim 10,characterized in that in the formation of the film thicknesses of from0.3 μm to 10 μm are produced.
 13. A process for the lithographicproduction of negative structures for the μm -and -nm range according toclaim 11, characterized in that the drying is conducted from 1 minutesto 60 minutes at from 60° C. to 120° C.
 14. A process for thelithographic production of negative structures for the μm -and nm rangeaccording to claim 10, characterized in that high pressure lamps orlasers are employed for the exposure.
 15. A process for the lithographicproduction of negative structures for the μm -and nm range according toclaim 10, characterized in that alkali metal ion-containing developershaving a concentration of from 0.2% wt. to 1.5% wt., or metal ion freedevelopers having a concentration of from 1% wt. to 5% wt. are employed.16. A process for the lithographic production of negative structures forthe μm -and nm range according to claims 10 or 15, characterized in thatthe time employed for development is from 10 seconds to 15 minutes.